Separation of wax by filtration with flue gas chilling



Dec. 25, 1951 w,'w KRAFT 2,579,501

SEPARATION OF WAX BY FILTRATION WITH FLUE GAS CHILLING Filed July 14, 1949 Patented Dec. 25, 1951 sriiiARKfi'iOii ofijvjigix BX FILTRATION W 'FLUE GAS GHILLiNG The Lummiis 'Gom'pan porznaion of Delaware y, New York, N. Y", a cor-- Th'i invention rlat "generally to @ijntiiitious rl'ie'thod for cooling the gases which 'aie employed in Solvent 'dew'aking filter 'opei'atiofi'.

It is generally known that the presefie' inert cold gaseous atmosphere in the filt'i' jadvanta-geous find present pra'cti; the ohillfed gets is bontinuouf's'ly used and recy'el'd. H weirer it picks 'up moisture and "sine it nnstb u dat temperatures bf the Oi'd'i' of 32 F, O i' 155$, T66 foi mationhas becoineh'seiious br'obl'efii'. abbbl'dahc with my iilVI'ifii'Ofi, I ll'bid the use of the usual shell and tube heat-geitbhajiigis heretdfo're employed the low tmpei'fitqre stage 01 6001111? and thlby' fivbid many "6f the operating difiicgltie which were g n ra ly ob"- ser ed; More 'pai t'i'cularly, y invention mates to the use of very large quantitie arso vent i'th regpect to the amount *of gas handled am; By 2 dift 6611115461) sewer, th' lfi' formed and carried away in the l q e J a to not materiauy reduce operating fliiiiy iiqi to indreajs'e opfating Co't'. H I have now fbunil, an econofiiiol new avoiding the difficulties inherent in th of flue gases This, is doneby suhjeetmg flue gases; to pri-mmafy cooling in alniiidi'reet heat exchange system to tempeiatuie my low fir t an the ice point, and "tn-en {nit iii-g in order to better uhdeitaiid the intention,

In carrying out the mventicsn, tli wag-wear ng oil is advantageously mixed with liquid or wax breeipitaiting irfed" veht liquid may comprise alight petiole flan such as haphthg, of other imi-ihus '0 B2 liquids or mixtures theifof, ketons; aidehyd'e, cyclib-hydi oarboii; b or its homologs. or derivatives of these varfon material It is foiind desirable 1:6 this firoes's for instance when a. sb1ii'nt i'I'h 5E acetone and ben'zol bi methfirl ethyl ketone, hfi 201, and toluol are-employed fol dew'aiii'ng The inii'itur or oil to be aewg'fed ahq the solvent liquid; cooled to iarbpe flit pr'at uie, 'onduted through line 11 in I2. Filter [2 is provided with smtitiibl' 11151111215 line [6;

m the filtering opiaft i'onaeui fing V 1%; the separated was; ma be vaauumonec and i-nemwas ea by means of 1 or hitam wash ng mum whih is drawn thiofi'gh into the meener of the arm; This imam is eastern-army with'diawn ream t l2 by independent means not shown, blit f be cbipbmed with the mug tie End mam throti'eh ne m if desired Va isuifip 1;; also communicates with filter l2 thi'oiih tank 1;; gnd line 4 and creates a vacuum wnhm me later |-2;. Thi's VaCun-m', appiied to th filter ta "e grte' washin permits drying the bake ndinj o d i j t gre tnrap' n; 'Sepaifatdwai: is ram :1 fi'on'i filtei' I; 5y suitable means not shown, through-1m T v may be inadvertently 1btpr13unias1 w diwn r'qm the system 1 Mamu ews itrodfieeuthfough line l1 into line l6 and ni' vaiiiim" pump I8.

packing material or it may contain shower trays or bubble decks.

Filtrate, from which gas has been separated,- is 5 drawn ofi from tank l5 through line 2'1, pump" 28, and line 29 to the upper part of the contact tower 25. Pump 28 is a low head pump. ,It will 1 be noted that the filtrate entering the tower 25 will be at approximately the same temperature as that in filter l2. gas will be dried and cooled to the filtering tem--: perature. This cooled fiue gas is withdrawn from .theoverhead to line 26 through which it is passed to filter R2. The pressure in tower 25 is sufii- ,eiently great so that the cooled gases may be passed directly to filter l2 without additional pumping. Proper lines and valves, not shown,

may be supplied at this point or elsewhere to al'lowfor drawing off any desired amount of cooled and dried flue gas from the system. v

' Proper by-pass lines and control valves, not shown, may be used to by-pass part of the filtrate 'aiound contact tower 25 if further control of the contacting operation is desired. Filtrate is removed from the bottom of tower 25 through line 30, pump 3|, and line 32. Pump 3| is a high head pump. Filtrate removed through line 32 passedinto a double pipe recovery system in which it cools the incoming solution in line H "from about 100 to 40 F. I f This novel system for cooling fiue gas has substantially the same power requirements as previous" processes. Low head pump 28 has a very low power consumption and high head pump 3| jissubstantially the equivalent of that employed by'the prior art to pump filtrate back to the double pipe' exchangers. Since much smaller amounts of heat exchanger surfaces are required, agreater'overall economy may thus be obtained. ,flnone system designed for operation according to this invention, a cold mixture of wax, oil, and solventat ''10 F. is fed into the filter [2 "through line H. Wax is removedthrough line 13' and approximately 200,000 pounds per hour of'filtrate are passed through line I4 to tank l5, Whereas filter l2 operates at a pressureslightly less than 6 pounds per square inch gauge, the tankWS is at a pressure of about 2 pounds per square inch absolute. Due to this difference in pressure, gas is separated from the liquid as it enters tank l5. I I iT'Ihisrecycle gas is withdrawn from tank [5 through line 10 and make-up gas which may be warm and may contain water is introduced through line I 1 into line It. The combined gases amounting to about 7800 pounds per hour along with entrained solvents and water are passed to vacuum pump IS. The gases are then cooled and chilled in cooler 20 and chiller 2| to about 40 F. After the condensed liquids are removed in gas-"liquid separator 22 and throughiline23, the gas is led into the bottom of tower 25. "Liquid is withdrawn from' tank l5 at a ternperature of about 10 F. This is pumped to the top of tower 25. It hasv been found most desirable to hold the ratio of liquid to gas in In contact tower t .25 will always be less than 5 F. and under most favorable conditions will be about2 F. This small temperature difference can readily be absorbed in the subsequent heat exchange operation and accordingly it does not detract from the advantageous features of this invention. *Thegases in turn are cooled from about 40 F. to 1 0, F. and simultaneously dried. The water, sin the form of ice, transferred to the filtrate -liquid amounts to about 13 pounds per hour for the 200,000 pounds per hour of filtrate.

These conditions may be modified to meet the specifications and requirements for any particular operation.

Thegas has been herein referred to for convenience as fiue gas. It is apparent, however, that it may include hydrocarbon vapor fixed gases such as nitrogen, or other appropriate constituents. i

While a vacuum type of continuous filter is generally employed, it is contemplated that this invention is equally well adapted to filtration under super-atmospheric pressure. The pressure in the contact tower will always be greater than the pressure in the filter, in order to pass dried gas to the filter without the use of an additional pump. I

This invention is not limited to the filteration of 'wax' from wax-bearmg oils, but is adapted to filtering other types of solid materials from liquids wherein it is desirable to maintain the resulting cake of solids at a temperature below that at which the solids tend to liquefy. Obviously many modifications and variations of the invention as hereinbefore set forth, may be made without departing from the spirit and scope thereof, and therefore only such limitations should be imposed as are indicated m the appended claims.

I claim: j

1. In a continuous process for separation of wax from a chilled mixture of wax, oil and solvent by filtration of said mixture in an atmosphereof fiue gas to produce a separated wax and a filtrate containing said fiue gas, the improvement whichcomprises withdrawing from the filtration operation filtrate containing said fiue gas, passing said withdrawn filtrate to a gas-liquid separating operation thereby separating flue gas contained in the filtrate and producing a denuded filtrate, introducing make-up gas to said separated flue gas, cooling the combmed make-up gas and flue gas to condense liquid therefrom, separating the condensed liquidsfrom said combined gas,,removing liquid from said gas-liquid separating operation, contacting said combined gas with said denuded filtrate, thereby further cooling the gas to the filtration temperature and simultaneously scrubbing the combined gas, and passing said cooled and scrubbed gas to the filtration operation. v

2. Inthe'proces's of claim 1 the improvements claimed'therein where the combined make-up gas andfiue gas is cooled to a temperature exceeding 32 F; in the first cooling step.

, 3. In the process of claim 1 the improvements claimed therein where the pressure in the contacting operation is greater than the pressure in w 5 4. In the process of claim 1, the improvements claimed therein where the temperature of the denuded filtrate leaving the contacting operation is below the ice point.

5. In the process of claim 1, the improvements claimed therein where the amount of Water in the denuded filtrate leaving the contacting operation is substantially below the quality required for saturation.

6. In a continuous process for separation of wax from a chilled mixture of wax, oil and solvent by filtration of said mixture at a temperature less than (3 F. in an atmosphere of flue gas to produce a separated wax and a filtrate containing said flue gas, the improvement which comprises withdrawing from the filtration operation filtrate containing said flue gas, passing said withdrawn filtrate to a gas-liquid separating operation thereby separating fluid gas contained'in the flltrate and producing a denuded filtrate, introducing warmer make-up gas to said separated flue gas, cooling the combined make-up gas and flue gas to a temperature exceeding 32 F. to condense liquid therefrom, separating the condensed liquids from said combined gas, removing liquid from said gas-liquid separating operation, contacting said combined gas with said denuded filtrate at a pressure greater than the filtration pressure, thereby further cooling the gas to the filtration temperature of less than F. and simultaneously scrubbing the combined gas, and passing said cooled and scrubbed gas to the filtration operation.

7. The process of claim 6 and the improvements claimed therein where the temperature rise of the denuded filtrate during the contacting operation is not more than 5 F. a

8. The process of claim 6 and the improvements claimed therein where the ratio of liquid to gas in the contacting operation is maintained at least 10 to 1 by weight.

9. In a continuous process for separation of wax from a chilled mixture of wax, oil, and solvent by filtration of said mixture at approximately -10 F. in an atmosphere of flue gas to produce a separated wax and a filtrate containing said flue gas, the improvement which comprises withdrawing from the filtration operation filtrate containing said flue gas, passing said withdrawn filtrate to a gas-liquid separating operation thereby separating flue gas contained in the filtrate and producing a denuded filtrate, introducing make-up gas to said separated flue gas, cooling the combined make-up gasand flue gas to approximately F. to condense liquid therefrom, separating the condensed liquids from said combined gas, removing liquid from said gasliquid separating operation, contacting said combined gas with said denuded filtrate at a pressure greater than the filtration pressure, thereby further cooling the gas to the filtration temperature of approximately -10 F. and simultaneously scrubbing the combined gas, and passing said cooled and scrubbed gas to the filtration operation.

10. The process of claim 9 and the improve- 'ments claimed therein where the filtrate comprises dewaxed oil and a solvent selected from the class consisting of methyl ethyl ketone.

benzol, and toluol and mixtures thereof.

WHEATON W. KRAFT.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

1. IN A CONTINUOUS PROCESS FOR SEPARATION OF WAX FROM A CHILLED MIXTURE OF WAX, OIL AND SOLVENT BY FILTRATION OF SAID MIXTURE IN AN ATMOSPHERE OF FLUE GAS TO PRODUCE A SEPARATED WAX AND A FILTRATE CONTAINING SAID FLUE GAS, THE IMPROVEMENT WHICH COMPRISES WITHDRAWING FROM THE FILTRATION OPERATION FILTRATE CONTAINING SAID FLUE GAS, PASSING SAID WITHDRAWN FILTRATE TO A GAS-LIQUID SEPARATING OPERATION THEREBY SEPARATING FLUE GAS CONTAINED IN THE FILTRATE AND PRODUCING A DENUDED FILTRATE, IN THE FILTRATE AND PRODUCING A DENUDE FILTRATE, GAS, COOLING THE COMBINED MAKE-UP GAS AND FLUE GAS TO CONDENSE LIQUID THEREFROM, SEPARATING THE CONDENSED LIQUIDS FROM SAID COMBINED GAS, REMOVING LIQUID FROM SAID GAS-LIQUID SEPARATING OPERATION, CONTACTING SAID COMBINED GAS WITH SAID DENUDED FILTRATE, THEREBY FURTHER COOLING THE GAS TO THE FILTRATION TEMPERATURE AND SIMULTANEOUSLY SCRUBBING THE COMBINED GAS, AND PASSING SAID COOLED AND SCRUBBED GAS TO THE FILTRATION OPERATION. 